Absorber arrangement for a trough collector

ABSTRACT

The invention relates to an elongated absorber arrangement for a trough collector, which is subjected to concentrated radiation over its length during operation, and which has means for transporting heat-transporting fluid through the absorber arrangement. The absorber arrangement has at least one fluid-free absorber space for concentrated radiation, which has a thermal opening leading into its interior and walls for absorption of the heat incident into it. The means for transporting the fluid have a supply arrangement and a drain arrangement which are operatively connected to one another by means of a heat-exchanger arrangement through which fluid flows, wherein the same extends along the length of the absorber arrangement, is constructed for the throughflow of the fluid in transverse flow for the length of the absorber arrangement and is thermally connected to the at least one absorber space in such a manner that the fluid is heated during operation in transverse flow from an inlet temperature to the operating temperature and reaches the drain arrangement at this temperature.

The present invention relates to an absorber arrangement for a troughcollector plant according to the preamble of claim 1. Trough collectorsof the stated type are used among other things in solar power plants.

Until now it has not been possible to generate solar electricity in anapproximately cost-covering manner by using this technology, owing tothe disadvantages of photovoltaics which have not been overcome. Bycontrast, for some time, solar power plants have already been producingpower on an industrial scale at prices which, compared to photovoltaicmethods, are close to the commercial prices now usual for power producedin the conventional manner.

In solar thermal power plants, the radiation of the sun is reflected bythe concentrator of collectors and focused in a targeted manner on alocation in which high temperatures arise as a result. The concentratedheat can be conducted away and used to operate thermal engines such asturbines which in turn drive the generators which generate electricity.

Three basic forms of solar thermal power plant are currently in use:dish/Stirling systems, solar tower plant systems and parabolic troughsystems.

The dish/Sterling systems as small units in the range of up to 50 kW permodule have generally not caught on.

Solar tower plant systems have a central absorber which is mounted in anelevated manner (on the “tower”) for the sunlight which is reflected toit by means of hundreds to thousands of individual mirrors, whereby theradiation energy of the sun is concentrated in a punctiform manner inthe absorber by means of the many mirrors or concentrators and onaccount of the thus achievable high concentration, temperatures of up to1300° C. can be reached, which is favourable for the efficiency of thedownstream thermal engines (generally a steam or fluid turbine powerplant for electricity generation). Solar tower power plants havehitherto likewise not become widespread (in spite of the advantageouslyachievable high temperatures), due to the somewhat difficult technologywhich is intrinsic to them.

Parabolic trough systems are widespread however and have a large numberof trough collectors which have long concentrators having smalltransverse dimensions and therefore do not have a focal point but afocal line, which fundamentally distinguishes these in their design fromthe dish Stirling and solar tower power plants. These linearconcentrators today have a length of 20 m to 150 m whilst the width canreach 5 m or 10 m and more. An absorber line for the concentrated heat(up to nearly 500° C.) is arranged in the focal line, wherein a medium,which absorbs the heat and transports the same via lines to the machinehall of the power plant, flows through the absorber line. A fluid suchas e.g. thermal oil or superheated steam are possibilities for theheat-transporting medium.

The 9 SEGS parabolic trough plants in Southern California togetherproduce an outlet of approx. 350 MW. The power plant “Nevada Solar One”,connected to the mains in 2007, has trough collectors with 182,400curved mirrors, which are arranged on an area of 140 hectares, andproduces 65 MW. The plants Andasol 1 to 3 should have a maximum outletof 50 MW (Andasol 3 entered into operation at the end of 2011). For theplant as a whole (Andasol 1 to 3), a peak efficiency of approx. 20% andalso an annual average efficiency of about 15%.

Naturally, it is the case that attempts are being made to increase thetemperature in the heat-transporting medium to the greatest extentpossible, as with the high temperature thereof, the efficiency of theconversion of the heat obtained in the plant into electricity forexample is higher. As high temperatures as possible are also desired incase the solar power plant is to deliver heat for processes ofindustrial production.

For the efficiency of the power plant, the emission or radiation of heatvia the lines in which the heat-transporting medium circulates (heatloss). is to be taken into account This may reach 100 W/m, with a linelength of the order of magnitude of up to 100 km, so that the heatlosses over the lines are of considerable importance for the overallefficiency of the power plant, also including the absorber pipes'proportion of heat losses. From the above information, it follows thatthe entire length of the trough collectors and accordingly also that ofthe absorber pipes in such solar plants reaches dozens of kilometres,thus the heat losses thereof cannot be neglected for the efficiency ofthe plant as a whole.

Accordingly, the absorber lines are built increasingly complexly inorder to avoid such energy losses. Thus, widespread conventionalabsorber lines are constructed as a metal pipe enveloped by glass,wherein a vacuum prevails between the glass and metal pipe. The metalpipe conveys the heat-transporting medium in its interior and isprovided on its outer surface with a coating which better absorbs theincident light in the visible range, but has a deep emission rate forwavelengths in the infra-red range. The enveloped glass pipe protectsthe metal pipe from cooling by means of the wind and acts as anadditional barrier for heat radiation. It is disadvantageous that theenveloping glass wall partly likewise reflects or even absorbs incidentconcentrated solar radiation, which means that a layer reducing thereflection is applied to the glass.

In order to reduce the expensive cleaning outlay for such absorberlines, but also in order to protect the glass from mechanical damage,the absorber line can additionally be provided with a mechanicalprotection pipe which envelops it and which although it must be suppliedwith an opening for the incident solar radiation, otherwise protects theabsorber line very reliably.

Such designs are complex and relatively expensive, both in terms ofproduction and in terms of maintenance.

In WO 2010/078 668 (which is here included in the present application byway of reference) an externally-insulated absorber pipe with improvedefficiency is disclosed, the elongated thermal opening of which existson account of the use in a trough collector and is constructed as a slotopening and is optimised with regards to the heat losses, in that thethermal opening is made smaller over the length of the absorber pipe inaccordance with the longitudinally-increasing temperature of theheat-transporting medium which flows longitudinally through the absorberpipe. As heat radiation increases with the fourth power of thetemperature, an overwhelming part of the overall energy losses of theabsorber pipe are prevented in this manner, even though the complexmeasures for making the thermal opening smaller are only performed in acomparatively small area of the absorber pipe.

It is the object of the present invention to provide an absorberarrangement suitable for high operating temperatures of theheat-absorbing medium, which absorber arrangement has low heat lossesand can be produced inexpensively in series.

This object is achieved by means of an absorber arrangement according tothe characterising features of claim 1.

The fact that a heat exchanger arrangement, which is constructed for thethroughflow of the heat-transporting fluid in transverse flow, isprovided means that the absorber space can be constructed in such amanner by means of the separation of the at least one absorber spacefrom the heat exchanger, through which fluid flows, that even at hightemperatures of more than 500° C., for example up to 650° C. or evenhigher, the heat radiation through the thermal opening thereof falls toa lesser extent and as a result, the efficiency of the heat-exchangerarrangement as a whole is improved.

The invention is explained in more detail hereinafter by means of thefigures.

In the figures:

FIG. 1 shows a trough collector with an absorber pipe of conventionaltype,

FIG. 2 shows a view onto a section of a first embodiment of the absorberarrangement according to the invention,

FIG. 3 shows a view onto a section of a second embodiment of theabsorber arrangement according to the invention,

FIG. 4 shows a view onto a section of a third embodiment of the absorberarrangement according to the invention,

FIG. 5 shows a view onto an absorber space formed by a part of theheat-exchanger arrangement,

FIG. 6 shows a cross section through a trough collector with an absorberarrangement according to the invention, which has at least two parallelmutually adjacently arranged longitudinally running absorber spaces, and

FIG. 7 shows a cross section through the absorber arrangement of FIG. 6.

FIG. 1 shows a trough collector 1 of conventional type, with aconcentrator 2 which is parabolically curved in cross section andreflects incident solar rays 3, wherein the reflected rays 4 areconcentrated into a focal line region in which an absorber pipe 5 isarranged. Via a supply line 6, the absorber pipe 5 is fed with aheat-transporting medium which flows through the same, is heated in theprocess from an inlet temperature T_(E) to an outlet temperature T_(A)and finally is conducted away by means of a drain 7.

Schematically illustrated links 8 allow the pivoting of the concentrator2 about the pivot axis 10, so that the concentrator 2 can constantly bemade to track the current position of the sun. Bearings 11 for theconcentrator 2 and the lines 6, 7 are likewise schematicallyillustrated.

In the graph D, the profile of the temperature T of theheat-transporting medium over the length L of the absorber pipe 5 isqualitatively illustrated by means of the curve 15. The temperaturecurve 15 is essentially linear, in accordance with the heat suppliedevenly over the length L to the absorber pipe (and thus the fluidflowing longitudinally through the same) by means of the reflected rays4.

The absorber pipe 5 has a thermal opening, which is not illustrated soas not to overload the figure, through which the rays pass into theinterior of the absorber pipe 5 and heat the heat-transporting fluid. Anarrangement of this type is known to the person skilled in the art fromthe above-mentioned WO 2010/078 668. The interior of the absorber pipe 5(including the heated heat-transporting fluid) heated by the reflectedrays 4 radiates heat in the infra-red range, wherein this heat backradiation or reemission escapes from the absorber pipe through thethermal opening. This back radiation or reemission increases with thefourth power of the temperature prevailing in the interior of theabsorber pipe 5. The curve 16 qualitatively shows the profile of theradiation intensity through the thermal opening of the absorber pipe 5.In other words, it is the case that the absorber pipe continuously losesenergy with the fourth power of the internal temperature thereof, sothat a fundamentally desirable further increase of the outlettemperature T_(A) from 500° C. to for example 650° C. or more isproblematic, because, among other reasons, the back radiation orremission is just as high after a certain length of the absorber pipe 5as the irradiation by means of the reflected rays 4, so that a furtherincrease of the temperature in the fluid no longer takes place.

FIG. 2 schematically shows an absorber arrangement 20 according to thepresent invention, as can be used in the place of the absorber pipe 5 ina trough collector (FIG. 1). Only a longitudinal section 21 of theabsorber arrangement 20 is illustrated in the figure, starting with across section through the absorber arrangement 20 at any desired pointalong the length thereof and a view of the longitudinal section 21through to a section line 22 following the cross section, wherein theabsorber arrangement 20 continues after the section line 22 through tothe end of the respective trough collector. At this point, it may beadded that absorber arrangements in a length greater than 100 m,preferably greater than 150 m and preferably up to 200 m or more may berealised according to the invention, which allows correspondingly longtrough collectors and is beneficial for the industrial deployment oftrough collectors in a solar power plant.

Visible are means for transporting the heat-transporting fluid, with asupply arrangement, here constructed as pipelines 23, 24, and a drainarrangement, here constructed as pipelines 25, which extend along thelength L of the absorber arrangement and are operatively connected toone another by means of lines, here constructed as pipelines 26. Thepipelines 26 here lie next to one another in two rows 27 and 28 and forma heat-exchanger arrangement 29. The row 28 is indicated by means of thecontours of the mutually adjacent pipelines 26, the row 27 is covered inthe view illustrated.

Between the rows 27, 28 of pipelines 26 of the heat-exchangerarrangement 29 lies an absorber space 30 for concentrated, i.e.reflected radiation 4, through the thermal opening 35 of which, the rays4 fall. Walls 36 of the absorber space 30 absorb the heat of the heatincident by means of the rays 4 and pass this on to the pipelines 26 ofthe heat-exchanger arrangement 29, to which they are thermallyconnected, for example by means of direct contact with the walls 36, asis illustrated in the figure.

During operation, heat-transporting fluid is supplied to the pipelines26 of the heat-exchanger arrangement 29 over the length L with the inlettemperature T_(E) by means of the inlet sections 38 of the pipelines 23,24 of the supply arrangement, wherein the fluid is heated to the outlettemperature T_(A) in the pipelines 26 and is passed at this temperaturefrom the outlet sections 39 to the pipeline 25 of the drain arrangement,likewise over the length L of the absorber arrangement.

In other words, it is the case that

-   -   in one embodiment of the invention, the supply arrangement and        the drain arrangement have a supply pipe 23, 24 and a drain pipe        25, wherein the pipes 23, 24, 25 run parallel to one another and        the at least one absorber space 30 is arranged between pipes 23,        24, 25 and extends over the length of the pipes 23, 24, 25.    -   In one embodiment of the invention, the supply arrangement has a        feed line 23, 24 for the fluid to be heated and supplied to the        heat exchanger over its length, which feed line extends over the        length of the absorber arrangement, wherein the feed line 23, 24        is preferably thermally insulated over its length through to the        openings for the supply of the heated fluid. This may be        advantageous if the inlet temperature T_(E) is above the ambient        temperature.    -   In one embodiment of the invention, the drain arrangement has a        collecting line 25, extending over the length of the absorber        arrangement, for heated fluid supplied to it over its length        from the heat-exchanger arrangement 29, wherein the collecting        line 25 is thermally insulated over its length through to the        openings for the supply of the heated fluid.

It follows that the heat-transporting fluid flows longitudinally throughthe absorber arrangement as before, but it two separate flows, once withthe inlet temperature T_(E) and once with the outlet temperature T_(A),as is symbolised by the flow arrows in the figure. Furthermore, itfollows that the heat-transporting fluid is moved in a directioncrosswise to the length of the absorber arrangement during theabsorption of heat.

In the heat-exchanger arrangement however, the fluid flows in transverseflow to the length L, with the consequence that over the entire length Lof the absorber arrangement 20 in the line 25 of the drain arrangement,fluid with the outlet temperature T_(A) is present. The followingadvantages result by means of this transverse flow principle:

The absorber space 30 can be laid out once in terms of its shape by theperson skilled in the art in such a manner that for a given concentrator2 (FIG. 1), principally the inlet region of the absorber space 30 isilluminated by the rays 4. In the inlet region close to the thermalopening 35, the fluid has another low temperature close to the inlettemperature T_(E), with the consequence that the inlet region isstrongly cooled, thus the heat reflection/reemission thereof iscorrespondingly low. With regards to reemission, the thermal opening 35overwhelmingly “sees” the inlet region, much less however the (far away,rearmost) wall of the absorber space 30 which is opposite the inletregion and for its part is heated to the outlet temperature T_(A). Theabsorber spaces illustrated in the figures are constructed beneficiallyin this respect.

At this place one can add that of course it is advantageous for allembodiments according to the present invention to cover the thermalopening e.g. by a glass cover in order to reduce the heatreflection/reemission.

On the other hand, it is the case that by shaping the absorber space(here principally the height thereof or, as seen in the direction of therays 4, the depth thereof) the person skilled in the art can achieve theenlargement of the heat-exchanging surface. For example, it is the casethat the entire inner surface of the pipelines 26 of the heat-exchangerarrangement is used as heat-exchanging surface. Although only one sideof the pipelines 26 is irradiated by the radiation 4, the pipelines 26are heated virtually evenly all the way round by the conduction of heatin the material of the pipelines 26 (for example a good heat-conductingmaterial such as copper or a suitable alloy, conducting heat well athigher temperatures), so that the heat-exchanging surface iscorrespondingly large. A large heat-exchanging surface is used for theefficient heat transfer to the heat-transporting fluid, so that a localoverheating of the heat-exchanging surface can be substantiallyprevented.

Here, mention may be made of the fact that according to the insight ofthe applicant, in conventional absorber pipes, at the end region (regionof high temperature of the fluid), the walls heated by the radiationoften overheat severely with the consequence that the reflection ismassively increased. The reason for this lies in the longitudinal flowof the fluid to be heated, which is already strongly heated itself inthe high-temperature region of the conventional absorber pipe and theheat-exchanging walls, thus during the short time in which it flowsthrough the end region, the walls of the end region can no longer coolsufficiently. (An increase of the mass flow is not possible, as the samemust reach its set point temperature T_(A) with a given heat input bymeans of the reflected radiation 4; were the mass flow to be increased,this temperature could no longer be reached).

As a result, it is the case that although in the case of the absorberarrangement according to the invention, a heat reflection or reemissioncorresponding to the outlet temperature T_(A) prevails due to thethermal opening 35, as, due to the transverse flow principle,overheating occurs scarcely or only to a small extent, the energy lossesin the absorber arrangement according to the invention are, all thingsconsidered, lower than in the case of the conventional absorber pipe.Accordingly, the absorber arrangement can be realised in virtually anydesired length L, without this having negative consequences with regardsto the heat radiation. In addition, in comparison with a conventionalabsorber pipe, even the heat reflection corresponding to the outlettemperature T_(A), as due to the geometry of the absorber pipe, relevantparts of the heat-reflecting or reemitting walls are kept cool.

It follows that according to the invention, the relevant wall regions ofthe absorber pipe located close to the thermal opening remain cooler andan overheating of the heat-exchanging surfaces is substantially reducedthan in the case of a conventional absorber pipe.

At this point, it may also be added that with the term “thermalopening”, depending on the design of the absorber pipe, is designated asa physical opening for the absorber space according to FIG. 2. The term“thermal opening” also comprises a physically closed region in the caseof other designs of the absorber space, which region is designed for thepassage of heat of the concentrated solar radiation, wherein forexample, by means of suitable coatings at the location of the heatirradiation, a reflection of the heat can be minimised. Designs of thistype are known to the person skilled in the art. Nonetheless, it isnecessarily the case, that at the location of the thermal opening,ultimately it is not possible to achieve good insulation, thus thecorresponding relevant heat losses due to heat reflection/reemissionmust be accepted.

Further, it may be added that the absorber arrangement according to theinvention can be used in a trough collector only a short distance fromthe edge thereof, for example after the fluid has reached a temperatureof 100° C. or somewhat more. An absorber arrangement according to thepresent invention extending over the entire length of the troughcollector is preferred however.

Here, it may be mentioned that the pipelines 26 of the heat-exchangerarrangement 29 can replace the walls of the absorber space 30 at leastto some extent, with the advantage that as a result, the pipelines 26are directly irradiated, that is to say the heat transfer to theheat-transporting fluid is only impeded minimally. It is likewisecompliant with the invention if at least sections of the wall of the atleast one absorber space are formed by the heat exchanger or thepipelines thereof. Further, it is compliant with the invention that theheat exchanger has mutually adjacent line sections for the fluid, whichform at least one wall section for the at least one absorber space.

In the embodiment illustrated in FIG. 3, the absorber space may forexample be formed by lines 42 of the heat-exchanger arrangement, as thesame run in mutually adjacent windings and thus preferably completelyenvelop the interior of the absorber space.

FIG. 3 shows a further embodiment of the absorber arrangement 40according to the present invention, which essentially corresponds tothat of FIG. 2, except for the construction of the heat-exchangerarrangement 41, whose lines, which are constructed as pipelines 42, arehere laid in small loops, that is to say are constructed longer in eachcase. In spite of these loops running in the longitudinal direction, theheat-exchanging fluid flows through the heat-exchanger arrangement 41 intransverse flow with respect to the longitudinal direction L. The tube24 (FIG. 2) is omitted in the FIG. 3, in order to make it possible tosee the pipelines 42.

Longer pipelines 42 have the advantage that the heat-exchanging surfacefor the partial flow of the fluid is enlarged, but the disadvantage thatthe pressure drop in the pipeline 42 is larger. In an actual case, theperson skilled in the art can determine the flow and thermodynamicdesign of the pipelines 42. Fundamentally any suitable conveying of theheat-transporting fluid by means of the heat-exchanger arrangementcomplies with the invention, as long as the conveying takes place in themain direction thereof transversely to the length L by means of theheat-exchanger arrangement in such a manner that the fluid is heatedduring operation from an inlet temperature to the operating temperaturein the transverse flow and achieves the drain arrangement. Likewise,generally any suitable construction of lines in the heat-exchangerarrangement according to the invention, which is used for passing thefluid, is compliant with the invention.

The small flow arrows 44 show the direction of flow of the heattransporting fluid.

FIG. 4 shows yet a further embodiment of an absorber arrangement 50according to the present invention, which essentially corresponds tothat of FIG. 2, except in turn for the construction of theheat-exchanger arrangement 51, whose lines, which are constructed aspipelines 52, are here laid in small coils 53, that is to say areconstructed even longer in each case. The coils 53 are only indicatedschematically in the Figure and illustrated in detail in FIG. 5.

The coils 53 formed from the pipelines 52 are open towards the bottomand as a result form absorber spaces 54, as a space section is enclosedby them. As a result, the heat-exchanging surface for this room sectionand thus also over the length of the absorber arrangement 50 getssubstantially larger, with the advantages as mentioned above for FIG. 1.The regions of the coils 53 open at the bottom form thermal openings 59.

The absorber spaces 54 lie in a row 55 due to the shown arrangement ofthe coils 53.

In FIG. 4 also, the pipeline 24 has been omitted so as not to overloadthe figure, so that the view onto the coils 53 becomes clear.

The result is that the absorber arrangement 50 in the embodimentillustrated in the figure is constructed in such a manner that thesupply arrangement and the drain arrangement have a supply pipe 23, 24and a drain pipe 25, wherein the pipes 23, 24, 25 run parallel to oneanother and the here numerous absorber spaces each formed by a coil 53are arranged between these pipes 23 to 25 and extend over the length ofthe absorber arrangement 50.

FIG. 5 shows a view of one of the coils 53 only indicated schematicallyin FIG. 4, formed from the windings of a line of the heat-exchangerarrangement 51 according to the invention, here constructed as apipeline 52. The coil 53 here has an axis of symmetry 55 and encloses anabsorber space 54 for the incident radiation 4, wherein the end of thecoil 53 which is open at the bottom forms a thermal opening 59.Heat-transporting medium at the inlet temperature T_(E) flows throughthe connecting piece 57 of the pipeline 52 into the coil 53, flowsthrough the same and is passed through the end section 58 of thepipeline 52 at the outlet temperature T_(A) into a collecting line, hereconstructed as pipeline 25.

Together with FIG. 4, an absorber arrangement results, in which thesupply arrangement and the drain arrangement have a supply pipe 23, 24and a drain pipe 25, wherein the pipes 23, 24, 25 run parallel to oneanother and a number of absorber spaces 54 is provided, which arearranged in at least one row 55 running between these pipes 23, 24, 25,wherein the at least one row 55 extends over the length of the pipes.Thus, advantageously generally a plurality of absorber spaces (anydesired configuration) are provided, which are connected parallelbetween the supply and the drain arrangements.

FIG. 6 shows a cross section through a trough collector 60, with anabsorber arrangement 61 according to the invention, wherein twoconcentrators 62 and 63 are provided, which are for example configuredaccording to WO 2010/037 243 (which is here included by reference in thepresent application). The framework of the trough collector 60 is forexample constructed in accordance with WO 2009/135 330.

In accordance with the two concentrators 62, 63, the absorberarrangement 61 has at least two absorber spaces 64 and 65 which extendover the length L of the absorber arrangement 61. However, it is alsocompliant with the invention to provide two rows of absorber spacesarranged one behind the other, analogously to the embodiments accordingto FIGS. 3 to 5, in which absorber spaces arranged in rows areillustrated. At this point, it may be added that it is likewisecompliant with the invention to provide more than two rows of absorberspaces in an absorber arrangement in the case of trough collectors witheven more mutually adjacent concentrators.

FIG. 7 shows a cross section through the absorber arrangement 61 of FIG.6. Illustrated is a line of a supply arrangement for heat-transportingfluid, constructed as pipeline 72, a heat-exchanger arrangement 74, herewith two rows, and also a pipeline of a drain arrangement for theheat-transporting fluid, which is here constructed as a collecting lineand is provided with insulation 70. In the embodiment illustrated, theheat-exchanger arrangement 74 has two rows 75 of spirals 53 arranged onebehind the other, as illustrated in FIG. 5. The fluid passes through theline 72 at the inlet temperature T_(E) to the connecting pieces 57 andas a result into each coil 53, passes through the same and leaves thesame via the end sections 58 of the pipeline 52 at the outlettemperature T_(A) and thus passes into the pipeline 25 of the drainarrangement. Preferably, there are secondary concentrators 73 known tothe person skilled in the art as trumpets, which run along the thermalopenings 59 over the length L of the absorber arrangement 61 in asuitable manner and thus concentrate the radiation already concentratedby the concentrators 62, 63 in the transverse direction of the troughcollector a second time in the transverse direction, which makes itpossible to reduce the width of the thermal openings.

Frame and structure elements 71 support the arrangement shown in thefigure and can be constructed suitably in an actual case by the personskilled in the art.

In the case of an embodiment not illustrated in the figures, a number ofabsorber spaces lying one behind the other in a row is provided over thelength of the absorber arrangement, which absorber spaces are arrangedseparated from one another at a distance from one another. Such anembodiment is advantageous if the radiation reflected by at least oneconcentrator (FIG. 1) or by a plurality of concentrators 62, 63 (FIG. 6)is concentrated longitudinally upstream of the absorber arrangement by afurther arrangement of longitudinal concentrators, so that instead of afocal line region, a number of focal point regions (wherein one or aplurality of longitudinally extending rows of focal point regions arepossible) are present with greater concentration.

Coils modified compared to the coils 53 shown in FIG. 5 are likewisecompliant with the invention. These may for example form an ellipticalor polygonal absorber space instead of a round one, or be terminated atthe wall opposite the thermal opening with a simple lid in the place ofthe coils of the pipe 52 shown in FIG. 5. (Likewise, the absorber spacesmay for example consist of one box in each case in the place of thespaces formed by lines).

Likewise compliant with the invention are coils, the axis of symmetry ofwhich is inclined with respect to the thermal opening (and notperpendicular according to the illustration in FIG. 5), with theadvantage that such coils are advantageous for a skew angle range. Theskew angle is known as such to the person skilled in the art anddesignates the angle at which the sun falls onto the concentratororientated towards it.

In summary, it is the case that according to the invention, theheat-exchanger arrangement and thus the at least one absorber space canbe adapted and configured in terms of design in accordance with thethermodynamic requirements present in the actual case, but theheat-exchanging fluid is heated in the transverse flow to operatingtemperature, i.e. to the outlet temperature T_(A), so that the drainarrangement is fed fluid at the outlet temperature A_(T) at the length Lthereof. The person skilled in the art can combine the featuresexplained in the above-described various embodiments depending on therequirements in the actual case, as these are not restricted to therespectively shown embodiments. Likewise, the heat-exchanger arrangementmay not only be formed by pipelines, but rather also by means of anothersuitable construction.

Finally, it is advantageous for reasons of pressure supply and accordingto a further embodiment of the invention to segment the supplyarrangement, wherein each segment has a connection for a fluid source.As a result, energy losses on account of the pressure drop in a longline are minimised.

1. An elongated absorber arrangement for a trough collector, which issubjected to concentrated radiation over its length during operation,with means for transporting heat-transporting fluid through the absorberarrangement, the absorber arrangement comprising: at least onefluid-free absorber space for concentrated radiation which has a thermalopening leading into its interior and walls for absorption of the heatincident into it, and the means for transporting the fluid have a supplyarrangement and a drain arrangement which are operatively connected toone another by means of a heat-exchanger arrangement through which fluidflows; and wherein the same extends along the length of the absorberarrangement, is constructed for the throughflow of the fluid intransverse flow for the length of the absorber arrangement and isthermally connected to the at least one absorber space in such a mannerthat the fluid is heated during operation in transverse flow from aninlet temperature T_(E) to the operating temperature T_(A) and reachesthe drain arrangement at this temperature.
 2. The elongated absorberarrangement according to claim 1, wherein a number of absorber spaceslying one behind the other in a row are provided over the length of theabsorber arrangement, which absorber spaces are directly adjacent to oneanother.
 3. The elongated absorber arrangement according to claim 1,wherein a number of absorber spaces lying one behind the other in a roware provided over the length of the absorber arrangement, which absorberspaces are arranged separated from one another at a distance from oneanother.
 4. The elongated absorber arrangement according to claim 1,wherein at least sections of the wall of the at least one absorber spaceare formed by the heat-exchanger arrangement.
 5. The elongated absorberarrangement according to claim 1, wherein the heat-exchanger arrangementhas mutually adjacent line sections for the fluid, which form at leastone wall section for the at least one absorber space.
 6. The elongatedabsorber arrangement according to claim 2, wherein an absorber space isformed by a line of the heat-exchanger arrangement, which run inmutually adjacent windings and thus preferably completely envelop theinterior of the absorber space.
 7. The elongated absorber arrangementaccording to claim 1, wherein the drain arrangement has a collectingline, extending over the length of the absorber arrangement, for heatedfluid supplied to it over its length from the heat-exchangerarrangement, wherein the collecting line is thermally insulated over itslength through to the openings for the supply of the heated fluid. 8.The elongated absorber arrangement according to claim 1, wherein thesupply arrangement has a feed line for the fluid to be heated andsupplied to the heat-exchanger arrangement over its length, which feedline extends over the length of the absorber arrangement, wherein thefeed line is thermally insulated over its length through to the openingsfor the supply of the heated fluid.
 9. The elongated absorberarrangement according to claim 1, wherein the supply arrangement and thedrain arrangement have a supply pipe and a drain pipe, wherein the pipesrun parallel to one another and the at least one absorber space isarranged between such pipes and preferably extends over the entirelength of the absorber arrangement.
 10. The elongated absorberarrangement according to claim 1, wherein the supply arrangement and thedrain arrangement have a supply pipe and a drain pipe, wherein the pipesrun parallel to one another and a number of absorber spaces is provided,which are arranged in at least one row running between such pipes,wherein the at least one row preferably extends over the entire lengthof the pipes.
 11. The elongated absorber arrangement according to claim1, wherein a plurality of absorber spaces are provided, which areconnected parallel between the supply and the drain arrangements. 12.The elongated absorber arrangement according to claim 1, wherein thesupply arrangement has a supply pipe which is segmented and wherein eachsegment has a connection for a source of heat-transporting fluid. 13.The elongated absorber arrangement according to claim 1, wherein thelength thereof is greater than 100 m, preferably greater than 150 m andparticularly preferably 200 m or more.
 14. The elongated absorberarrangement according to claim 1, wherein secondary concentrators areprovided, which concentrate the incident radiation in the longitudinaldirection of the absorber arrangement upstream of the at least oneabsorber space.